Magnetic material, process of producing it, and electromagnetic device incorporating such material



June'19, 1928.

, F. -B'ANDURll L, PROCESS OF lPRODUCING' IT f A. MAGNETIC MATERIA l A DEVICE INCORPORATING -SUCH MATERIAL 1 ...u C 1 u w A W M 6 O e M S L 2 E D N A 1,673,790 A. 4F. BAN-DUR 'MAGNETIC MATERIAL, PROCESS OELPRODUCING IT, AND ELECTROMAGNETIC DEVICE INCORPORATING SUCH MATERIAL Y y Filed ne. 13. 1924 2 sheets-sheet 2 Jufie 19, 192s.

Patented vJune A19, A'1928...

UNITED STA c im-,190+

TESIPATENT OFFICE.

ADOLPH FRANCIS BANDUiaOF :BERWYN ILLINOIS, AssIeNon To WESTERN ELECTnIC COMPNY, INCORPORATED, OE NEW YORK, N. Y., A CORPORATION OE NEW YORK.

RocEss OE PRODUCING IT; AND ELECTnOnAGNETIC DEVICE MAGNETIC MATERIAL, P

INCOB-PORATNQ SUCH MATERIAL.

Application filed December 13, 1924. Serial No. 755,813. l

- Thisinvention relates to magnetic ma- .teria1s', processes of producing them, and electromagnetic devices 1n whichy such materials ih aylbe used to advantage.

The principal object of the invention isfto secure constancy of operating characteristics ot magnetic material used in signaling apparatus and for other apparatus employing low lield strengths; examples of slgnaling upparatus.- heilig inductlve loading, transformers, relays, filter coils, and balancing and waveshapingynetvvorks.

Au object of the inventlon'ma dierent aspect is to reduce, 'in magnetic material used in signalingl appara-tus, variations 1n th'ose magnetic characteristics the variabilityA of which introduces distortion 1n the signall ing currents. Two such characteristics are permeability and variable flux duel to hysteresis.' Another .object is to secure relatlve `constaney of the `variable Operating characteristic-s in magnetic material used in signalingapparatus and for apparatusemploying low field strengths, and atthesame time to secure a high value ot' permeability: .An-

other object is to obtain in a magnetwmatcrial thoie characteristics which' peculiarly adapt. it foruse asinductive loading material forsignaling lines. Other objects of the invention will become apparent on consideration of the following specification.

' Wlherevcr magnetic material is subjected to `magnetic fields set up 'by 'signaling currents, these currents are distorted because ries within the operatingv range'.

' but this effect is ordinarilyy small.

there isjno known magnetic .material which does -not have some characteristic which va.

Such distortion isvariously characterized as modulation, Morse flutter, etc., .depending upon they conditionsunder which it is produce-d. .Permeability vordinarily varies With the field strength or Withthe resultant flux density. Likewise, when fields due to av lcomplete cycle of 'alternating signalingA current are set up, the flux density is diHerent for equal positive and negativevalues of the lield strength because of theV hysteresis of lthe m'agncticmatcrial. The resistivity may likewise vary somewhat with field. strength which introduces variable losse-s withi consequent distortion of the signaling current, It is highly desirable to have high'resistivity to avoid excessive eddy current losses and lalso to have high permeability to enable a given 'inductance to be obtained with a mimmum -amount ofthe material.

- In British Patent.189,410 is described an invention of G. W. Elmen pertaining to nickel-iron alloys which in many respects are more suitable for vinductive loading than iron. Such alloys may contain from 25% or 30% to around 80% or more of nickel,

A the preferred' proportions being nickel 7 815% and iron 211/%. A heat treatment suitable for obtalnlng lngh permeability, lowv hysteresis loss and hlgh resistivity is there cle-- scribed. l

The present invention is the outgrowth-of` an extension of vtheinvestiggntion leading to the invention disclosed in the British Patent 189,410. It is based upon the discovery that when nickel-iron alloys containing from 30% to 60% of nickel are given a'special treatment hereinafter described, the permeability becomes relatively constant over a very wide ran e of low flux densities-the range ordinari y employed in signaling'- and, as compared with iron, the permeability is high, 'the hysteresis loss very low,"

and the reslstivity very high. The material .is better than iron in all of these important respects.

I-leretofore, aside from'the work of Elmen, various investigators have independently investigated some of the .propertles of certain nickel-iron alloys falling withinthe range .from 330% to A60% nickel but not at flux densitieswith `vvhich this invention is concerned.

The treatment of nickel-iron alloys employed to obtain ythe properties described above may be outlined as follows: The alloy ingot, after casting, is worked by bein rolled and occasionally 'annealed as foun necessary until thin sheets or strips about .002 inch thick are obtained. This process produces a certain moderate degree of hardness 1n the'metal. It is then subjected to a vtemperature lower than that which would simultaneously increasing one oi these facf.

tors and-decreasing the other. The proper"- values of temperature and time may be determined by trial in each case. The rate of cooling is preferably morey rapid than that ordinarily employed in' annealing but has no critical value. Cooling in air at ordinary room temperature is satisfactory. The process of subjecting a material, as just described,

to a temperature and for a time insuticient:

- to secure maximum softness is herein char- -acterizedfas partially annealing. A

'In the valloy justV mentioned containing y 36% of nickel lwhen treated as described, permeability will lie in the rangerom I125 to 1000 4and the variation'of permeability over i a range Aof flux densities from to 100 c. g. s.

units is from 2% -to 5%., The hysteresis loss at a maximum flux density of 8 c. g. s. units may be Aas low'as 1.5'10-4 ergs per cycle per bm, being about A1/ 15th that of hard drawn iron wire. The resistivity is about 80 microhms per cm3.

Inductive loading of signaling l-ines is a suitable use of magneticmaterial to serve as .an illustration of the uses and manner of the following specification.

preparation ofthe new material, and has therefore been chosen for thatpurpose in Hereto-fore the material which has been i' generally used for loading telephone lines scribed, for example, in 'an article by Buckyc. g. s. units.

is iron, theinos't suitable. form being specially prepared compressed iron dust. Another'1 form is that in which the core is a coil ot fine iron wire. Such 'loading coils are dener Speed and G. WfElmen, entitled Magnetic properties of compressed powdered iron.l Journal .of the A. I. EE., July, 1921.

In the construction of loading coils for telephone lines-in which thelcores are of iron wire, it has been foundpossibleto obtain a -semi-hard drawn wirewhich has an initial magnetizing torce corresponding to a tele-` phone current of live milliamperes is of the order of .05 gauss. At a permeability of 100 the corresponding iiux density is v5 c. g. s.l

units. Ordinarily, however. loading'must be .designed to serve either near the terminals of lines or cables where the currents are large or at mid-line where the. currents have been reduced by attenuation. In many installations, moreover. vtelephone and telegraph currents are composited so that the 4 iiux in the coils at any given point on the line varies over a wide range. Inv man v other uses of mag'netizing material designed to operate at flux densities up too 100 c. gis.-

units, the flux varies over a large part of this range, as for example in transformers employed tointerconnect stages of amplifiers 'permeability of 'the new magnetic material over a range of iux densities from 0 to 100 c'. g. s units, compared to thegrade of iron having the greatest attainable constancy of` permeability over this range;,

Fig. 3 is a representative .curve showing the initial. permeability that will be secured in one form of the improved magnetic material for certain definite heat treating temperatures Fig. 4'is arepresentative curve showing the magnitude of the hysteresis loss that may 4be secured in a piece of thenew magnetic material after being subjected to the several temperatures of heat treatment shown on the graph; and

.Fig 5 shows the percentage change in permeability that occurs when the maximum HuX density is changed from 0 to 100 c. g. s. units for the improved alloy after having been subjected to the different heat treatments indicated on the graph. f

In preparing the material for use as the core of a loading coil, nickel and iron in the proportion, for example, of about 36% nickel andthe balance of iron are fused in an induction or arc furnace. Pure commercial grades of these two metals are suitable for this purpose. Thev molten alloy is poured into an ingot mold and allowedto solidify. The ingot is then subjected to repeated hot rolling operations followed by cold rolling operations by which it is reduced in thickness and correspondingly elongated to have a final thicknessof about .002 inch. The strip is then passed through cutting rolls or discsfwhich trim its edges squarely on both sides to give t-liestrip an eXact'and uniform width of 1 inch. Thistape of nickel-iron composition is then rolled up to form a ring core as shown-in Fig. 1. the adjacent convolutions thereof being suitably insulated-from each other. In insulating these adjacent turns of the ring corel` good results have been secured by subjecting the tape to an oxidizing 'process prior to wrapping it into the ring in the manner just described. This skiclizing process consists in removing all oil and grease from the tape with alcohol the final heat treating temperature (to be' described hereinafter). The duration of this process depends upon the thickness of the oxide coating desired, but good results have been secured by heating the material to the temperature stated tor about 15 minutes.

The. core is then heat treated for a period of time and to a temperature less than would be required for completely annealing it and is then cooled. For example, it has been 'found desirable to heat the core to a temperature of approximately 480 C. and maintain it at this temperature for about. 15 minutes, the core then being allowed to cool. Experin'ients have indicated that thc rate ot cooling is not critical and good rcsults have been secured by accelerating the cooling by placing thc core in a cold air blast. l

Ithas been found desirable to impregnato the core after heat treating by immersing it under partial vacuum in ahot molten insulating compound that solidities on cooling. 'lhe core after immersion is removed from the molten compound and allowed to drain and cool. This provides a rigid and substantialcoil. A rosin compound consisting of a mixture of rosin and rosin oil in ratio of three to one has given good results.

For example. to term a loading coil having an inductance ot' 28 milhenries and an efl'ective resistance ot less than 3.0 ohms with a 1800 cycle alternating current of .002 amperes flowing through a winding of approximately 285 turns of number 22 copper wire, 12 pound ot the strip prepared in the manner heretofore described'is rolled into a tight ring core the interior opening of which has a diameter of about 1.375 inches, the ends of the coil being held in any suitable manner.

T he parti-cular value of permeability desired in the material will vary, depending upon the uses to which the material is to be put, and in order to secure any particular value of permeability which will be constant over a wide range of low flux densities, the temperature during the heat treatment is raised to a definite point. Generally stated, the higher the permeability desire-d the higher the temperature to which-the heating is carried.

Fig. 3 shows the initial permeabilities that will be secured for a range of heat treating tempe atures of a nickel-iron alloy having Kil/2% nickel, the heat treatment having a duration of 15 minutes. In this figure, permeabilities are plotted as ordinates and temperatures as abscissae, it being understood that the shape ot the curve will depend somewhat upon the amount and kind of mechanical treatments to which the vmaterial is subjected while 4being worked down to its final dimension. In general the same type of curve will be obtained for other periods of application of the heat treatment,

the longer the period't-he lower the temperature at which thev maximum point. ot' the curve will occur. The change, thus produced by prolonging the period beyond a few hours is not marked.

Fig. 4 shows the magnitude ot the hysteresis loss obtained for a range of heat treating temperatures with a nickel-iron alloy having W1/2% nickel, the heat treatment in each case having a duration of 15 minutes. This figure shows hysteresis loss in ergs per cycle per cm3 for a maximum flux density of 8 c. g. s. unitsl as ordinates. 'lhe heatl treating temperatures are shown as abscissae.

One ot' the outstanding characteristics of this improved magnetic material is the small change in permeability that occurs with changes in flux densities below 100 c. g. s. units. By the method of heat treatment herein described it is possible to secure smaller changes in permeability for given changes in flux density below l0() c. g. s. units than when the material is either una-nnealed or fully annealed. By referring to Fig. 5 it will be apparent the way in which the method otI heat treatment herein described reduces the percentage cha-nge in permeability. The curve of Fig. 5 is representative and lnay shitt'- up or down or laterally depending on the previous history y ot the material.

In Fig. 2 are curves showing the varia.- tions of permeability with flux density for the most suitable grade of iron in comparison with the improved magnetic alloy. v By referring to curve A which is representative of the form of iron having the most constant permeability over this range, and to curve B representative of the improved magnetic material in the form of nickeliron alloy, the comparative constancy oi-, permeability of the materials over a wide range of low flux densities is disclosed. Percents of initial permeability are'plotted as ordinates and ux densities as 'abscissae Curve B is for a nickel-iron alloy having 371/2% of nickel.

A coil such as that above described is about one-third or less the volume of the best loading coils designed for the same purpose now in use.

It is obvious that the material just described is adapted for continuous loading of signaling conductors as Well as for loading coils. As compared with loading material in which high permeability is developed by heat treatment after the material, in a form suitable for continuous loading, is placed upon the copper conductor, the material of this invention has the advantage that if heat treatment of the loaded conductor becomes desirable or necessary the temperature required will be relatively low and will not necessitate special precautions in the loading of lines employing high frequency, since distortion known .as intermodulation is then large when ordinary materials are used.

It is within the scope of this invention to apply to any magnetic materialthe treatment herein described, modified to suit the particular material and the degree to which the desired characteristic or characteristics are to be obtained, for the purpose of obtaining the desirable results hereinspecified. In another aspect, the invention comprehends the material so treated. i e

The nickel-iron alloys herein mentioned consist essentially of nickel and' iron but material having an initial permeabilitysubstantially greater than 125 and1 having a per- -meability over a range of iux densities from 0 to 30 c. g. `s. units within 2% of its initial other elements may be present in small,` permeability, -v'izvhich comprises hardening amounts. The range of nickel-iron alloys of this invention from 35% to 38% of nickel is particularly suitable for loading and analogous purposes, 36% nickel beingperhaps the best, but the invention is applicable throughout the lentire range from 30% to of nickeland may be used to advantage for some purposes in the range from 60%- -to 80% or 90% of' nickel'.

What is claimed is: 1. The method of producing a magnetic -material ofrelatively. high initial permeability and relatively constant permeability over al selected range of magnetizing forces, which comprises heating'the material at a temperature lower and for a period of time shorter than isrequired to completely anneal the material. 2. The method of producing a magnetic material in accordance with claim 1 characterized in this that the magnetic material is composed of nickel and iron. A

3. The method of producing a magnetic .material in accordance with claim 1 characterized in this that the nickel content is and partially' annealing the material.

7. The method of producing al magnetic material in accordance with claim 6 characpermeability and having a substantially constant permeability over a range of flux densities. from Oto 100 c. g. s. units, which o consists in hardening and incompletely annealing the material.

` In witness whereof, I hereunto subscribe my name this 2nd day of December A. D., 1924.

ADoLPH FRANCIS BANDUR. 

